Sterility Testing

The compendial sterility test introduces product into two growth media, one favouring anaerobes and one favouring aerobes and fungi, either by direct inoculation or by filtering the product through a membrane that is then incubated. The media are held for fourteen days and examined for growth. The test destroys what it examines, so it is performed on a sample of units drawn from a batch and never on the batch itself.

That sampling is the central limitation. A negative result across a few tens of vials cannot distinguish a fully sterile batch from one with low-frequency contamination, which is why assurance is built into the process instead: filtration through a 0.22 micrometre membrane, aseptic filling in a classified environment, and periodic media fills that challenge the filling line under production conditions. Terminal sterilisation gives a far stronger guarantee, but most peptides cannot survive autoclaving.

Sterility is therefore a property of a validated process that the test confirms rather than creates. It is also narrow. The test detects viable organisms and says nothing about endotoxin, the heat-stable lipopolysaccharide fragment released when Gram-negative bacteria die, which needs its own amebocyte lysate or recombinant factor assay and survives every sterilisation method that kills the organism producing it.

Conflating sterile-filtered with sterile is the error that recurs. Passing a solution through a filter in an uncontrolled room and dispensing it into non-sterile containers produces neither a sterile product nor any basis for the claim. Research-use vials are commonly not sterile and not labelled as though they were, and a certificate showing a sterility pass with no endotoxin result leaves the more probable contaminant entirely untested.